Flexible unbonded pipes of the present type are for example described in the standard “Recommended Practice for Flexible Pipe”, ANSI/API 17 B, fourth Edition, July 2008, and the standard “Specification for Unbonded Flexible Pipe”, ANSI/API 17J, Third edition, July 2008. Such pipes usually comprise an innermost liner also often called an inner sealing sheath or an inner sheath, which forms a barrier against the outflow of the fluid which is conveyed in the bore of the pipe, and one or more armor layers. In general flexible pipes are expected to have a lifetime of 20 years in operation.
Examples of unbonded flexible pipes are e.g. disclosed in WO0161232A1, U.S. Pat. No. 6,123,114 and U.S. Pat. No. 6,085,799.
The term “unbonded” means in this text that at least two of the layers including the armor layers and polymer layers are not bonded to each other. In practice the known pipe normally comprises at least two armor layers located outside the innermost sealing sheath and optionally an armor structure located inside the innermost sealing sheath normally referred to as a carcass.
These armor layers comprise or consist of multiple elongated armor elements that are not bonded to each other directly or indirectly via other layers along the pipe. Thereby the pipe becomes bendable and sufficiently flexible to roll up for transportation.
In traditional flexible pipes the armor layers often comprise metallic armor layers including a pressure armor layer of helically wound wires and cross-wound tensile armor layers of wires wound with a lower angle.
In the prior art it has been suggested to replace one or more of the metallic armor layers with armor layers of fibres or fibre reinforced polymer of different structures. U.S. Pat. No. 6,165,586 for example discloses a strip of filamentary rovings of glass fibre or aramid fibre sampled with bonding material and retaining means. It is suggested to use such strips to replace one or more metallic armor layers of an unbonded flexible pipe.
WO 01/51839 discloses a flexible unbonded pipe comprising a tensile armor layer of aramid fibres embedded in a thermoplastic material.
U.S. Pat. No. 7,842,149 discloses a method of manufacturing a precursor for a reinforcement element for a flexible pipeline. One or more precursors are thereafter laminated with each other and/or other strength-imparting layer or layers to form a final reinforcement element. This provides the advantage that the individual strength-imparting layers in the reinforcement element may be manufactured as an independent product which may be stored and later be included in the manufacture of a reinforcement element for a flexible pipeline.
In the production of a pipe with the reinforcement element of U.S. Pat. No. 7,842,149, the reinforcement layer is composed by applying a number of strength-imparting layers with a coating of thermoplastic polymer to the pipe. Immediately prior to winding on the pipe, the strength-imparting layers are heated, causing the applied thermoplastic polymer to melt. Thereby the strength-imparting layers fuse to a unit. Since this fusion takes place immediately prior to the application to the pipe, the thermoplastic polymer will be molten during the winding, but will harden immediately after the application to the pipe. As a result, after solidification the applied element will essentially have a shape that ensures a low level of residual stress in the strength-imparting layers and that the unit formed by the strength imparting layers has either the final helical shape or a shape which will allow for final deformation to helical shape with only moderate extra force.